Bath for the galvanic deposition of gold and gold alloys, and uses thereof

ABSTRACT

The invention relates to a bath for the electrodeposition of gold and gold alloys and to its use for producing dental moldings. In this bath, the gold is in the form of a gold sulfite complex. The bath according to the invention and/or the use according to the invention is distinguished by the fact that in addition to the optional presence of further metals and standard additives for gold sulfite baths of this type, there is at least one bismuth compound. This bismuth compound is preferably a complex compound, in particular with the complex-forming agents NTA, HEDTA, TEPA, DTPA, EDNTA or EDTA.  
     The invention has a whole range of advantages associated with it. One advantage which should be particularly emphasized is that the addition of bismuth can be added to the bath as early as during its preparation. This means that the user is provided with a bath which is able to function for a prolonged period of time and to which it is not imperative to add further additives prior to the electrodeposition.

[0001] The invention relates primarily to a bath for electrodeposition of gold and gold alloys and to its use. In this bath, the gold is in the form of a gold sulfite complex.

[0002] It has already been known for a very long time to electrodeposit gold or gold alloys from preferably aqueous solutions which contain the gold and/or the corresponding alloy metals. After predominantly cyanide-based gold baths were initially used, in recent times baths based on gold sulfite complexes have been becoming increasingly important. This trend was attributable primarily to the fact that the gold sulfite baths are non-toxic compared to the cyanide-based gold baths in which hydrogen cyanide is known to be released. This non-toxicity and the good quality of the layers deposited has led to the gold sulfite baths being used to an ever increasing extent, in particular in the field of dental technology, despite their higher production costs and despite the problems with the stability of the baths. Furthermore, baths based on gold sulfite complexes are relatively easy to handle, which is an important factor for users without high levels of specialist chemical engineering knowledge, such as dental technicians, dentists and their staff.

[0003] Particularly in the field of dental technology, particular demands are imposed on deposits formed by electroplating. In addition, these demands also vary according to the type of dental frame or prosthetic molding produced. For example, a homogenous layer build-up, i.e. a homogenous microstructure, a layer thickness which is as uniform as possible and a reproducible composition of the deposited layer are preconditions if it is subsequently to be possible for a ceramic or plastic veneer to be applied to the molding. This applies in particular to ceramic veneers, for which the molding has to be fired at relatively high temperatures after the ceramic material has been applied. In these cases, the metallic basic framework also has to have the required firing stability. Minimum demands also have to be satisfied with regard to further properties, such as wear resistance, porosity, corrosion resistance, inter alia. Moreover, the layers deposited, in particular in the dental sector, have to comply with particular aesthetic requirements, for example relating to the color, the shine or the surface condition. Finally, certain further demands may be imposed on the composition of the deposited layers, for example with regard to biocompatibility. Biocompatibility of the materials may be particularly important especially in the dental sector, since gold or gold alloy layers with the maximum possible purity are required for example for patients suffering from allergies.

[0004] Irrespective of their field of use and irrespective of the form in which the gold is present in the bath, gold and gold alloy baths contain certain additives in order to at least partially comply with the requirements imposed on the electroplated deposits. Additives of this type are also known as fine-grain additives or shine additives. These may be organic additives, such as polyamines, polyimines and mixtures thereof or semimetal compounds, for example of arsenic, antimony or thallium. All the additives mentioned may be incorporated to a greater or lesser extent in the deposited gold layer. In the case of the organic additives, this causes problems in the dental sector, since the layer properties (e.g. ductility and firing stability) may be adversely affected by this incorporation. The incorporation of the semimetals causes problems in the dental sector in particular in the case of arsenic and thallium, since the required biocompatibility is then no longer ensured on account of the use of these toxic substances. The result of this is that, as far as the Applicant is aware, currently only antimony has gained any significance as an additive in the dental sector. However, in physiological terms it is by no means undesirable for the antimony compounds used to be replaced. However, when prosthetic moldings are being lined with dental ceramic, no metal compounds other than antimony compounds have proven suitable for reasons of firing stability.

[0005] A further problem involved with the use of previously known additives for gold and gold alloy baths, in particular for baths based on gold sulfite complexes, is that these additives generally have to be metered in immediately before the baths in question are used. This is because the compounds which are present in these additives are not stable in the baths in question, but rather decompose over the course of time, losing their effectiveness. This may be caused, for example, by the pH of the baths in question or by the fact that the additives react with other constituents contained in the bath.

[0006] In the case of the addition of antimony compounds to baths based on gold sulfite complexes, the antimony is generally used as Sb(III), for example as potassium antimony tartrate. The latter reacts in the bath to form jelly-like antimony oxide hydrate gel, which is likely to destroy the action of this additive. For its part, the antimony oxide hydrate gel is not stable under the standard bath conditions and reacts to form crystalline antimony oxide, which no longer reveals the desired effect. This is the reason why the additive can only be added to the bath just before use and why the additive loses its effect after a certain time.

[0007] Consequently, it is not possible to produce a gold or gold alloy bath comprising all the required components which is able to function over a prolonged period of time.

[0008] A further problem is that the additives not only have to be metered in at a later stage, but also that the correct metering, i.e. the required quantity of additive, is dependent on the other bath and process parameters. Factors of influence in this context are, for example, the proportions of the other constituents in the bath, the concentration of the electroactive ions, the geometry of the deposition vessel (cell geometry) the temperature and the current density. In most cases, the user attempts to solve these problems by, on account of his lack of specialist chemical engineering knowledge, working according to what is known as a metering table provided by the manufacturer of the bath and measuring the quantity of additive as a function of the number of objects to be electroplated. Since the size and shape of the objects which are to be electroplated and the desired layer thickness of the deposit vary considerably, and accordingly so does the quantity of metal to be deposited, metering per object in this way is subject to a relatively high error level. This can lead to very varying qualities of the electroplated deposits, and consequently even objects which have been coated at the same time in a single operation may differ in terms of the composition of the deposit. This can make deposition difficult for the user to manage.

[0009] EP-B1 0 126 921 has described an aqueous bath for the electrodeposition of gold-copper-bismuth alloys that contains the gold in the form of a gold cyanide complex. This involves the deposition of ternary alloys with high bismuth contents. The bath described in that document is particularly suitable for the deposition of pink-to violet-colored coatings on decorative objects, such as for example jewelry, watches and spectacles. The technical significance is supposed to lie in the fact that the bismuth can be incorporated in the alloys in extremely high levels of up to 30% by weight and above. This is intended to open up new application areas, such as for example the treatment of electronic components, such as plug connections, since the corresponding deposits are particularly hard and have a good electrical conductivity and resistance to abrasion. The baths described in EP-B1 0 126 921 are unsuitable for the dental sector, inter alia both on account of their high toxicity and on account of the fact that high levels of the bismuth are to be incorporated in the alloy.

[0010] DE-C2 2 723 910 (corresponds to FR-A 2353656) claims a multiplicity of additive mixtures for baths for the electrolytic deposition of gold or gold alloys. These additional mixtures are intended to improve the properties of the deposits formed. Compulsory constituents of these additive mixtures are at least one organic water-soluble nitro compound of a certain general formula and at least one water-soluble metal compound of an element selected from the group consisting of arsenic, antimony, bismuth, thallium and selenium. Additive mixtures which, in addition to the nitro compound, also contain a water-soluble bismuth compound are in this case too restricted to use in cyanide-based baths. In the case of baths based on a gold sulfite complex, this document proposes the use of an additive comprising nitro acid and antimony-potassium double tartrate. The use of the additive mixtures mentioned in DE-C2 2 723 910 and of the gold baths produced therefrom is restricted to the technical application of plating electronic components for semiconductor technology.

[0011] Furthermore, U.S. Pat. No. 5,277,790 has disclosed an additive for a bath based on a gold sulfite complex which likewise has to contain both an organic polyamine or a mixture of polyamines and an aromatic organic nitro compound. DE-A1 3 400 670 describes a bath based on gold sulfite complex which contains an additive comprising water-soluble thallium salt and a carboxylic acid which is free of hydroxyl and amino groups.

[0012] The invention is based on the object of providing a bath for the electrodeposition of gold and gold alloys which at least partially avoids the drawbacks outlined above. In particular, it is intended to make the production of prosthetic dental moldings by electrodeposition even more reliable and safer and to further simplify handling of the baths used for this purpose. Furthermore, it is intended to create the option of providing the user with a bath which has already been provided with all the required constituents and additives and is therefore able to function. Finally, the intention is for it to be possible for the baths in question to be operated substantially with biocompatible, i.e. physiologically harmless compounds without the quality of the layers deposited being adversely affected.

[0013] This object is achieved by the bath having the features of claim 1 and by the uses having the features of claims 20 and 21. Preferred embodiments of these subjects of the invention are explained in the dependent claims 2 to 19 and 22 to 27. The wording of all the claims is hereby incorporated by reference in the content of the present description.

[0014] The bath according to the invention for the electrodeposition of gold and gold alloys based on a gold sulfite complex is distinguished by the fact that in addition to any further metal compounds which may be present and other standard additives for such gold sulfite baths, it contains at least one bismuth compound. This bismuth compound is preferably a water-soluble bismuth compound, which results in the bath itself also preferably being an aqueous bath.

[0015] In principle, the bismuth compound used may be any suitable inorganic or organic bismuth compound. The bismuth compound is preferably a complex compound, preferably what is known as a chelate compound. Compounds of this type are known to be cyclic compounds in which a ligand (complex-forming agent) occupies a plurality of coordination sites of a central atom (metal), and consequently are generally particularly stable complex compounds. It is also preferable according to the invention if the bismuth compound contains an organic complex-forming agent, preferably an organic chelate-forming agent. Examples of complex-forming agents or chelate-forming agents in this context are in particular NTA (nitrilotriacetic acid), HEDTA (N-(2-hydroxyethyl)ethylenediaminetriacetic acid), TEPA (tetraethylene pentamine), DTPA (diethylenetriaminepentaacetic acid), EDNTA (ethylenedinitrilotetraacetic acid) and the preferred complex-forming agent/chelate-forming agent EDTA (ethylenediaminetetraacetic acid).

[0016] Other examples of bismuth compounds which can be used in accordance with the invention are water-soluble bismuth salts (e.g. sulfates, nitrates, sulfamates, phosphates, pyrophosphates, acetates, citrates, phosphonates, carbonates, oxides, hydroxides, inter alia). In addition to the preferred complex-forming agents which have already been mentioned above, such as NTA and the like, other examples of organic complex-forming agents which can be mentioned include: organic phosphonic acids, carboxylic acids, dicarboxylic acids, polyoxycarboxylic acids, hydroxycarboxylic acids, diketones, diphenols, salicylaldehydes, polyamines, polyaminocarboxylates, diols, polyols, dipolyamines, aminoalcohols, aminocarboxylic acids, aminophenols.

[0017] It is also preferable in the context of the invention if the bismuth compound (or if appropriate a plurality of such compounds) is(are) present in the bath in a concentration of between 0.05 mg/l and the saturation concentration of this(these) bismuth compound(s) in the bath. In particular, concentrations of between 0.05 mg/l and 1 g/l in the bath are preferred. Low concentrations are generally preferred, with concentrations between 0.1 mg/l and 10 mg/l being particularly useful within the latter range.

[0018] In a particularly preferred embodiment, the bath according to the invention is substantially free of additives which are physiologically harmful (harmful to health), the bath preferably being free of arsenic, antimony and thallium compounds. This ensures that there are no compounds, in particular metals, which are harmful to health and could restrict the usability of the layers or of the resulting prosthetic moldings in dental technology, incorporated in the deposited layers. Amazingly, it has also been found that the inventive addition of bismuth compounds is also in a position to reduce or even prevent physiologically harmful additives from being incorporated in the prosthetic molding. As has already been mentioned in the introduction, conventional gold sulfite baths contain at least one antimony compound as an additive. Accordingly, the antimony is incorporated in the prosthetic molding in a concentration of normally 0.2 part per thousand. If an antimony compound, such as potassium antimony tartrate, and a bismuth compound, such as bismuth EDTA, are used simultaneously, however, it has surprisingly emerged that both antimony and bismuth are present in quantities of less than 30 ppm or 40 ppm (these are the detection limits with the analysis method used for these elements) in the deposited molding. This shows on the one hand that the bismuth itself is not incorporated in the molding and on the other hand that the bismuth is able to considerably reduce the extent to which the antimony is incorporated.

[0019] The concentration of gold in the bath according to the invention is not fundamentally critical. It is preferable for the gold to be present in the bath in a concentration of between 5 and 150 g/l. In particular, gold concentrations of between 10 and 100 g/l, preferably between 10 and 50 g/l, in the bath are selected. A particular advantage of the invention is that it is possible to select gold concentrations in the bath of between 30 and 48 g/l. These relatively high concentrations make the bath according to the invention particularly suitable for the rapid deposition of thick layers, as is fundamentally desirable in the field of production of prosthetic moldings in dental technology. Particularly in the case of baths with high gold concentrations, it is possible to obtain prosthetic moldings with layer thicknesses of approximately 200 μm in less than 14 hours, preferably in less than 12 hours. It is even possible, given a suitable procedure, to deposit moldings with layer thicknesses of this type in less than 6 hours. The particular advantages of the invention also manifest themselves in particular in the case of deposition operations which are carried out in less than 2 hours, preferably within one to two hours. In this context, reference is also made to the examples.

[0020] In preferred embodiments of the invention, the bath contains at least one further metal. This metal can be incorporated in the deposited layer and is in these cases referred to as an alloying metal. However, in other cases it may also be used only for (improved) deposition of the gold or gold alloy layer. This metal may in particular be copper and/iron and/or at least one precious metal. If precious metals are added, precious metals from what is known as the platinum group are preferred, in particular palladium or platinum. Precious metals, in particular those belonging to the platinum group, are particularly suitable in the field of prosthetic dental moldings on account of their high biocompatibility.

[0021] By way of example, the concentration of the further metal in the bath can also be varied within wide limits as a function of the alloy which it is desired to deposit. In principle, the metals can be added in the form of their preferably water-soluble compounds, in particular salts, or in the form of preferably water-soluble complex compounds. In this context, it is once again possible to employ in particular the complex-forming agents and chelate-forming agents which have already been mentioned above in connection with bismuth. The concentrations of the metal compounds may preferably be selected to be between 0.1 mg/l and 200 g/l. Within this range, the concentration may be between 0.1 and 500 mg/l and in particular between 1 and 20 mg/l. In this case too, low concentrations are preferred. Concentrations of between 2 mg/l and 10 mg/l are further preferred within the latter range.

[0022] The gold sulfite complex in the bath according to the invention may in principle be any complex which is known from the prior art. It is preferably what is known as ammonium-gold sulfite complex, in which, therefore, the gold ion has been complexed by the sulfite ions and at least one ammonium ion is present at “counterion”.

[0023] The baths according to the invention preferably have a pH of at least 7, i.e. they are either neutral or alkaline. In particular, the baths are (weakly alkaline, with pHs of from 7 to 9 being preferred.

[0024] The preferred ammonium-gold sulfite complex has a range of advantages over other gold sulfite complexes. For example, compared to sodium/potassium-gold sulfite complexes, a significantly increased stability of the complex in the gold bath is responsible for a range of advantageous properties. These are, for example, a longer shelf life, reduced sensitivity to impurities and a lower light sensitivity. Moreover, baths comprising ammonium-gold sulfite complexes can be operated at a significantly lower pH of approximately 7-9. This makes baths of this type easier and safer for users with a lack of specialist chemical knowledge to handle compared to the Na/Ka-gold sulfite complex baths with pHs of approximately 10.

[0025] Surprisingly, a particularly advantageous relationship between chemical composition of the gold bath and chemical composition of the deposit formed by electrodeposition has resulted in the bath according to the invention which is based on the preferred ammonium-gold sulfite complex and contains at least one bismuth compound. This relationship is improved still further by the presence of the further metals in the gold bath, in particular of copper and/or at least one precious metal and/or iron. In addition, it has been possible to determine a widened range of applications, since in addition to plaster it is also possible to use a wide range of dental modeling and framework materials in the gold bath.

[0026] For example, the use of the bismuth compound has made it possible in an amazingly simple way to accurately control and predictably set the composition of the electroplated gold layer and its functional properties. This has hitherto been impossible or almost impossible with the known gold baths which are used in dental technology, and consequently with those baths the composition of the deposit is generally determined by technical factors, such as electrode geometry and the other apparatus technology factors.

[0027] As has already been mentioned a number of times, the demands imposed on a gold bath and the layers formed by electrodeposition are of a particular nature in the field of dental technology, and consequently in this sector, in addition to the requirements mentioned in the introduction, the need for biocompatibility and for the desired gold or gold alloy layers to be as pure as possible should be emphasized once again. For this reason, it is particularly important for the composition of the deposits formed by electrodeposition to be controlled in a targeted manner and set reproducibly.

[0028] Furthermore, in the case of the preferred further metal copper, it has emerged that in these preferred baths according to the invention a specific quantitative ratio between bismuth and copper is advantageous for the composition of the gold layer. A surprise in this context was that the standard parameters of influence in electrodeposition which are known to the person skilled in the art, such as for example electrode geometry, electrodeposition time, current density, temperature, form of current, etc., have only a minor effect on the deposition. Consequently, the copper content in the gold layer can be set accurately and reproducibly by setting the bismuth-copper ratio in the bath. The high level of purity which is advantageous for dental technology can therefore deliberately be achieved by targeted control of a low copper content in the layers without this adversely affecting the functionality of the layers. The targeted incorporation of low copper contents in the gold layer, while at the same time avoiding incorporation of bismuth, in addition to the high level of purity also enables the functional properties of the gold layer to be accurately controlled, such as for example the hardness, shine, surface properties, color, etc.

[0029] If gold layers which are as pure as possible are to be deposited with copper and bismuth present in the bath, the bismuth:copper ratio (based on the metals) is <1, in particular between 0.3 and 0.5. If alloys are to be deposited by the incorporation of copper, this ratio is >1.

[0030] In the case if iron as a further metal in the gold bath, surprisingly still further advantages have resulted in the bath according to the invention. Iron does not cause any problems in use and is even required by the body as an essential trace element. In addition, on the one hand by selection of the quantitative iron-bismuth ratio in the gold bath and on the other hand by selection of the type of iron compound/iron complex compound, it allows the composition and properties of the gold layer deposited to be controlled even more accurately.

[0031] By way of example, particularly advantageous gold layers resulted using the iron complexes Fe-DTPA, Fe-EDTA, Fe-EDNTA with quantitative bismuth-iron ratios from approximately 1.5 to approximately 2. By contrast, if iron citrate is used, an advantageous quantitative bismuth:iron ratio is approximately 0.18 to approximately 0.3.

[0032] In this context, the surprising observation that, despite the advantageous effect of the iron compounds during the deposition, no iron (<10 ppm) is incorporated in the gold layer, was of particular significance. This now even makes it possible, by way of example, to deposit gold layers with a purity of up to 99.99% and with excellent technical properties, such as for example absolutely reproducible firing stability, by electroplating. This was not hitherto the case with standard gold electrolytes which are able to deposit such pure layers.

[0033] A further surprise was that despite the different positions of copper and iron in the electrochemical series, it is also possible for the two metals to be used together, in a wide range of quantitative ratios with respect to bismuth, in the bath according to the invention. Therefore, the large number of possible combinations for the bismuth-copper-iron ratios opens up a wide range of options for new possible ways of controlling the properties, composition and function of gold and gold alloy layers formed from baths in accordance with the invention. In situations in which bismuth, copper and iron are simultaneously present in the bath, the quantitative bismuth:copper ratio is preferably >0.4 and the quantitative bismuth: iron ratio is preferably >0.3.

[0034] Furthermore, it has amazingly been found that in the bath according to the invention (including the bismuth compound and the interaction between the above-described additions of compounds of further metals in the gold bath), the reduction or prevention of the incorporation of physiologically harmful additives in the layer formed by electroplating, as described in the introduction, is nevertheless retained. Therefore, even when various metals, such as for example copper and/or iron, are present, the bath according to the invention is also able to selectively prevent the incorporation of, for example, antimony.

[0035] As mentioned above, the bath according to the invention may contain further standard additives which are customarily present in baths of this type based on a gold sulfite complex. Additives of this type are known to the person skilled in the art and can be varied in the standard ranges within the scope of his specialist knowledge. For example, conductive electrolytes with their conductive salts, buffer systems/buffer mixtures, what are known as stabilizers and wetting agents are present. If appropriate, brighteners and/or fine-grain additives which are known from the prior art may also be present in the bath according to the invention.

[0036] The invention also comprises the use of the bath according to the invention as described above for the production of prosthetic moldings for the dental sector by means of electrodeposition. A use of this type is intended in particular for the production of what are known as dental frames, such as crowns, bridges, superstructures and the like. The prosthetic moldings are in this case electrodeposited on a substrate. In this context, one also refers to the process known as galvanoforming. The self-supporting, stable molding is separated from the substrate and processed further. The substrate may, for example, be a cast molded from a tooth stump or an implant build-up part (prefabricated or individually prepared).

[0037] In a corresponding way, the invention also encompasses the use of at least one bismuth compound, preferably of at least one water-soluble bismuth compound, for the production of prosthetic moldings for the dental sector by means of electrodeposition. In particular, the bismuth compound is used as a constituent of a bath according to the invention as described above. Bismuth compounds which can preferably be used have already been explained extensively above, and consequently reference can be made to the corresponding parts of the description.

[0038] A particularly important feature of the invention which should be emphasized is that the bismuth compound which is used in accordance with the invention and if appropriate also the compounds of further metals can be added to the bath directly during its production. This means that the user is provided with a bath which is fully functional in terms of having all its constituents and additives. Unlike with the known baths from the prior art, the user does not have to meter in any additive before carrying out the electrodeposition process, which would entail the drawbacks which have already been explained above.

[0039] However, it is pointed out that the bismuth compound which is used in accordance with the invention may also be metered into the bath before or during the electrodeposition if desired. A variant of this type may also be provided, for example, when an aqueous bath to which a completely or partially water-insoluble bismuth compound, e.g. bismuth oxide, has been added during production is used. This water-insoluble compound can then be converted into a water-soluble bismuth compound immediately before or even during the electrodeposition by addition of a suitable complex-forming agent, and this water-soluble bismuth compound then reveals the desired action in the bath.

[0040] The situation in which the bismuth compound is added to the bath after an electrodeposition operation for top-up purposes should be mentioned as a further referred variant of the invention. This relates to the situations in which the concentration of gold and/or further metal in the bath is sufficient for a plurality, in particular a multiplicity, of deposition operations. In this case, the bismuth compound (and if appropriate also the compounds of the further metals) can be topped up appropriately for subsequent deposition cycles.

[0041] As has already been mentioned briefly, the use in accordance with the invention is intended for the production of prosthetic moldings which have sufficient stability in the galvanoforming process. Accordingly, it is customary to provide molding layer thicknesses of more than 10 μm. The layer thicknesses of the molding are preferably between 100 and 300 μm, with in particular layer thicknesses of approx. 200 μm being deposited. The provision of layer thicknesses of this type means that the invention is suitable not just for the production of crowns but also of bridges and other superstructures.

[0042] Finally, the invention also comprises a process for producing prosthetic moldings for the dental sector from gold and gold alloys by electrodeposition. This process is intended in particular for the production of dental frames, such as crowns, bridges, superstructures and the like. In this process, according to the invention, a gold or gold alloy layer is deposited on a suitable substrate from a bath in accordance with the invention, and the layer obtained is separated (demolded) from the substrate. As mentioned above, the substrate may, for example, be a cast which has been molded from a tooth stump or an industrially prefabricated or individually treated implant build-up part.

[0043] The substrate is preferably composed of an electrically nonconductive material, in particular plaster or plastic. This normally relates to situations in which a cast has been molded from the tooth stump. The surface of the nonconductive substrate is then made conductive prior to the electrodeposition, in particular with the aid of conductive silver.

[0044] In other preferred cases, the substrate is composed of at least one metal which is itself already conductive. In this case, examples of suitable substrates which may be mentioned are inner telescopes (usually made from a cast and milled dental alloy) or implant build-up parts, such as implant build-up posts. Parts of this type usually consist of titanium or titanium alloys.

[0045] The process according to the invention and also the uses according to the invention are preferably characterized in that the deposition takes place at high current densities, which usually results in short electrodeposition times. It is preferable to select current densities of up to 10 A/dm², in particular current densities of up to 8 A/dm². The bath according to the invention can still be used very successfully at such high current densities.

[0046] The use according to the invention or the process according to the invention can preferably be carried out in such a way that the deposition takes place using what is known as the pulse-plating process. This type of electrodeposition of metal likewise uses direct current. However, this direct current is applied as a pulsed current, i.e. in the form of current pulses which are interrupted by pauses. With regard to the prior art, reference can be made at this point, by way of example, to the “Pulse-Plating” volume from the series of papers entitled Galvanotechnik und Oberflächenbehandlung [Electroplating and Surface Treatment], Leuze-Verlag, Saulgau, 1990. The use of the pulse-plating process in dental technology is shown in DE-A1 198 45 506 in the name of the present Applicant, the content of which is in this respect incorporated by reference in the content of the present description. The use of the pulse-plating process in the present invention has the advantage that the deposits can be formed in the desired thickness, for example of approx. 200 μm, within relatively short times.

[0047] Furthermore, the use according to the invention and the process according to the invention are preferably characterized in that the prosthetic molding deposited is veneered with ceramic and/or plastic during its further processing. The desired tooth replacement is produced in this way. A molding which has been veneered with ceramic is fired in the usual way after the ceramic has been applied, for example at temperatures of up to approximately 950° C. A molding which has been veneered with plastic, after the plastic has been applied, is irradiated with light, in particular with visible light, in order for it to be cured, after the surface of the molding has previously been conditioned using suitable processes which are known to the person skilled in the art.

[0048] As has already been mentioned to some extent and as is also shown by the examples listed below, a wide range of advantages are associated with the invention.

[0049] For example, the bath according to the invention is eminently suitable for the production of prosthetic moldings (dental prostheses). The properties of the deposits are at least as good as those achieved with deposits formed from gold sulfite baths which operate, for example, with antimony compounds being metered in. The quality of the deposits in the bath according to the invention tends to match the specific requirements of dental technology even more successfully.

[0050] The pure gold layers obtained with the bath according to the invention are a golden yellow color and are extremely shiny, and therefore satisfy particularly high aesthetic demands. Of course, it is optionally also possible to produce matt and/or rough surfaces. The firing stability of these layers, which is imperative if they are to be veneered with ceramic, is provided with a reproducible reliability despite the fact that it is possible to dispense with an antimony compound in the gold bath. As far as the Applicant is aware, this has not hitherto been the case in any bath which is able to operate without an antimony compound.

[0051] A further advantage of the bath according to the invention is that it is clearly insensitive to plastics which have been introduced into the bath and are provided, for example, as tooth stump materials or to cover metallic parts which are not to be coated by electrodeposition. In the baths of the prior art, plastics of this type (cast molding plastics) or enamels (covering enamels) during deposition in the gold bath release constituents which have an adverse effect on the action of the fine-grain or shine additives of the gold bath. This adverse effect becomes more noticeable the higher the current density is selected to be during deposition. In the invention, this results in the advantage that, since the bath is insensitive to such disruptive influences, it is possible to operate at relative high current densities (cf. above, up to 8 A/dm² or 10 A/dm²).

[0052] It must also be mentioned that the efficiency of the bath according to the invention, for the same profile of demands imposed on the electrodeposited layers, is entirely comparable with conventional baths based on gold sulfite complexes which operate, for example, with antimony or arsenic additives. It is even possible to increase the efficiency compared to known baths if the bismuth additive is selected appropriately.

[0053] The possibility of dispensing with compounds which may be harmful to health, for example of arsenic, thallium and if appropriate also of antimony, in the bath according to the invention by using the bismuth additives has already been explained above.

[0054] Surprisingly, a further advantage of the bath according to the invention is found to be that a bath of this type with bismuth additive functions without problems, and in particular with above-average results, in various devices (including from a number of different manufacturers) which are in commercial use in the dental sector for electrodeposition. Hitherto, it has normally been necessary either for the composition of the gold or gold alloy bath to be precisely matched to the device used or for a device of this type to be precisely matched to a specific bath, in particular with regard to its process parameters. The result of this has been that each manufacturer has normally offered a specific gold bath for a very specific device whose process parameters have been matched to this gold bath.

[0055] With the bath according to the invention, it is now possible, for example, to operate various devices using this gold bath without these devices having to be adjusted to this bath in a complicated way. For example, an AGC micro-appliance produced by the present Applicant, which achieves a layer thickness of 200 μm usually in 12 hours, can be operated with the bath according to the invention equally successfully as an AGC MicroPlus appliance which achieves the same layer thickness in just 5 hours. The bath according to the invention is also suitable for use in devices which operate using the pulse-plating process, for example the AGC Speed appliance produced by the present Applicant. In devices of this type, layer thicknesses of 200 μm are achieved, depending on the size of the part which is to be electroplated, within 1 to 2 hours. Therefore, the bath according to the invention can advantageously be matched to existing electroplating deices owned by the user. The range of applications from “slows ” devices through to the “fastest” devices, which may also be operated completely automatically, illustrates how useful the invention is to the user.

[0056] Finally, it should be mentioned once again that the additive comprising a bismuth compound which is present in the baths according to the invention can be added as early as during preparation of the bath. The result of this is that the user is provided with a fully functional bath without being forced to add further additives prior to the electrodeposition process. Furthermore, it has emerged that the baths according to the invention with the bismuth additive are stable over prolonged periods of time. This means that the bath remains able to function even after it has been stored for prolonged periods and the additive does not lose its effectiveness. All this makes the bath easier to operate and more reliable when carrying out the electrodeposition process both for the manufacturer of the bath and for the user, since all the sources of faults which can occur with retrospective metering in excluded of additives are ruled out from the outset.

[0057] The features described and further features of the invention will emerge from the following description of preferred embodiments in conjunction with the subclaims. In this context, the individual features may in each case be realized on their own or in combination with one another.

EXAMPLES

[0058] Standard electrolysis cells which are known from the prior art and are commercially available can be used for the electrodeposition of prosthetic moldings made from gold or gold alloys which is carried out in accordance with the present examples. These electrolysis cells may, for example, be the AGC® devices produced by the present Applicant under the names “Micro”, “Micro 5h”, “Micro Plus” or “Speed”, depending on the desired procedure.

[0059] An electrolysis cell which can be used in accordance with the examples comprises a vessel for holding the bath. This vessel is usually provided with a cover. Furthermore, there is an anode, which may comprise a plurality of parts, and at least one cathode. The gold or gold alloy is electrodeposited on this cathode, which is formed, for example, by the substrate, such as a plaster stump or build-up post. The anode consists, for example, of platinum-coated titanium. A suitable current/voltage source is provided for the deposition itself. Furthermore, there is usually a magnetic stirrer with heating, which simultaneously ensures a constant (normally elevated) deposition temperature in the bath and is responsible for driving a magnetic stirrer rod which is present in the electrolysis cell. Accordingly, a temperature sensor is also introduced into the electrolysis cell.

[0060] It is expressly pointed out that the invention does not require any particular configuration of the electrolysis cell or of the apparatus which includes this electrolysis cell. The corresponding apparatus for deposition from gold sulfite baths are well known to the person skilled in the art.

[0061] As has already been explained in the description, in accordance with the examples (purely as a selection)

[0062] plaster stumps/plaster casts which have been made conductive using conductive silver,

[0063] cast and milled inner telescopes in which parts which are not to be electroplated are filled with a suitable plastic and the surface which is to be electroplated is covered with conductive silver,

[0064] build-up posts for the production of cap-like moldings which can be cemented to implant build-up posts, and

[0065] plaster casts which have a block for connecting two adjacent teeth and have likewise been coated with conductive silver, are electroplated.

[0066] Bath composition, deposition parameters, substrate and deposition result of the examples carried out can be found in Table 1. In all cases, the particularly advantageous bath based on an ammonium-gold sulfite complex was used.

[0067] In addition to the constituents listed, the baths used also contain standard additives for gold sulfite baths. These additives are known to the person skilled in the art. For example, they are conductive salts (sulfites, sulfates and phosphates), wetting agents or stabilizers, such as for example nitro acids. The bath according to the invention differs from the known baths in particular through the addition of the bismuth compound, and on account of this addition it is if appropriate possible (although not necessary) to dispense with additives which are present in conventional baths, such as for example antimony compounds or nitro compounds.

[0068] Where the deposition result in the following table refers to a “defect-free” functionality, this is intended to mean that the layer obtained during the deposition does not have any cracks, pores or holes. TABLE 1 Example 1 2 3 4 5 Bath Au 16.5 g/l 15.7 g/l 15.7 g/l 16.5 g/l 15.7 g/l composition Bi compound Bi-EDTA: Bi-EDTA: Bi-EDTA: Bi-EDTAL Bi-NTA: 1.2 mg/l 3.2 mg/l 2.5 mg/l 640 mg/l 2.5 mg/l Other Cu-EDTA: Cu-EDTA: Cu-EDTA: Cu-EDTA: Cu-TEPA: 5 mg/l 10 mg/l 10 mg/l 5 mg/l 10 mg/l Bi: metal Bi/Cu: Bi/Cu: Bi/Cu: Bi/Cu: Bi/Cu: ratio 0.24 0.32 0.25 128 0.25 Deposition Time 12 h 5 h 6.9 h 5 h 6.9 h parameters Mean current 0.5 A/dm² 1.5 A/dm² 1.5 A/dm² 1.5 A/dm² 1.5 A/dm² density Form of Direct current Direct current Direct current Direct current Direct current current Temp. 65° C. 65° C. 65° C. 65° C. 65° C. Substrate Type/quantity Plaster Inner Build-up post Plaster Plaster cast stumps; telescope made made from stumps; of a block; conductive from a dental gold-titanium conductive conductive silver gold casting alloy; silver silver alloy filled conductive with Pattern silver Resin (from GC); conductive silver Deposition Thickness 200 μm 200 μm 300 μm 200 μm 300 μm result Gold content >99.9% >99.9% >99.9% >99.99% >99.9% Bi content Bi < 40 ppm Bi < 40 ppm Bi < 40 ppm Bi < 40 ppm Bi: <40 ppm Alloy content — — — — — Efficiency of 82% 86% 86% 82% 86% the bath Appearance gold color, gold color, gold color, gold color, gold color, shiny; smooth shiny; smooth shiny; smooth matt; shiny; smooth uniformly covered with extremely fine buds Functionality defect-free; defect-free; defect-free; defect-free; defect-free; stable during stable during stable during the desired stable during the subsequent the subsequent firing in the roughness firing of the ceramic or processing and case of the deliberately subsequent plastic fully ceramic increases the ceramic veneer veneering functional as veneering and boundary a secondary suitable for surface area part cementing to with respect the implant to the veneer build-up post ceramic Example 6 7 8 9 10 Bath Au 48 g/l 40 g/l 100 g/l 15 g/l 8 g/l composition Bi compound Bi-HEDTA: Bi-EDTA: Bi-NTA: Bi-DTPA: Bi-EDTA: 5.9 mg/l 3.5 mg/l 6 mg/l 50 mg/l 5 g/l Other Cu-EDTA: — Cu-EDTA: Cu-EDTA: Cu-TEPA: 20 mg/l 15 mg/l 200 mg/l 20 g/; Bi: metal Bi/Cu: — Bi/Cu: Bi/Cu: Bi-Cu: ratio 0.295 0.40 0.25 0.25 Deposition Time 105 min 3 h 1 h 6.91 h 12 h parameters Mean current 3.6 A/dm² 2.0 A/dm² 10 A/dm² 0.5 A/dm² 0.5 A/dm² density Form of pulsed direct pulsed direct Pulsed direct Direct current Direct current current current; current; current; relative on relative on relative on time 86% time 86% time 88% Temp. 65° C. 65° C. 65° C. 65° C. 65° C. Substrate Type/quantity Plaster Plaster Plaster Inner Plaster stumps; stumps; stumps; telescope made stumps; conductive conductive conductive from a dental conductive silver silver silver gold casting silver alloy filled with Pattern Resin (from GC) conductive silver Deposition Thickness 200 μm 200 μm 200 μm 200 μm 200 μm result Gold content >99.9% >99.99% >99.9% >99.78% >95% Bi content Bi < 40 ppm Bi < 40 ppm Bi < 40 ppm Bi < 40 ppm Bi: 60 ppm Alloy content — — — Cu: 0.22% Cu: 5.0% Efficiency of 48% 50% 10% 86% 50% the bath Appearance gold colored, gold colored, gold colored, Gold colored, gold colored, shiny; smooth matt, smooth shiny; smooth extremely extremely shiny; smooth shiny Functionality defect-free; defect-free; defect-free; Defect-free; defect-free; during the stable during stable during stable during stable during subsequent the plastic the plastic the subsequent the subsequent ceramic veneering veneering processing and plastic veneering fully veneering functional as a secondary part Example 11 12 13 14 Bath Au 16.0 g/l 15.7 g/l 16.6 g/l 16.6 g/l composition Bi compound Bi-EDTA: Bi-EDTA: Bi-NTA: Bi-EDTA: 2.4 mg/l 5.39 mg/l 2.33 mg/l 4.5 mg/l Other Cu-EDTA: Cu-EDTA: Fe-EDNTA: Fe-citrate 10 mg/l 10 mg/l 1.53 mg/l 17.72 mg/l Antimony Fe-DTPA: tartrate: 1.26 mg/l 54 mg/l Bi: metal Bi/Cu/Sb: Bi/Cu/Fe: Bi/Fe: Bi/Fe: ratio 1/0.24/0.044 1/0.54/4.3 1/1.52 0.26 Deposition Time 5 h 5 h 5 h 5 h parameters Mean current 1.5 A/dm² 1.5 A/dm² 1.5 A/dm² 1.5 A/dm² density Form of direct current direct current direct current Direct current current Temp. 65° C. 65° C. 65° C. 65° C. Substrate Type/quantity Plaster Plaster Plaster Plaster stumps; stumps; stumps; stumps; conductive conductive conductive conductive silver silver silver silver Deposition Thickness 200 μm 200 μm 200 μm 200 μm result Gold content >99.9% >99.9% >99.9% >99.9% Bi content Bi < 40 ppm Bi < 40 ppm Bi < 40 ppm Bi < 40 ppm Alloy content Sb: <30 ppm Fe < 10 ppm Fe < 10 ppm Fe < 15 ppm Efficiency of 82% 86% 86% 86% the bath Appearance gold colored, gold colored, gold colored, Gold colored, shiny; smooth shiny; smooth shiny; smooth satin finish; smooth Functionality defect-free; defect-free; defect-free; Defect-free; stable during stable during stable during stable during the subsequent the subsequent the subsequent the subsequent ceramic or ceramic or ceramic or ceramic or plastic plastic plastic plastic veneering veneering veneering veneering Example 15 16 17 18 Bath Au 15.7 g/l 16.3 g/l 15.7 g/l 15.7 g/l composition Bi compound Bi-EDTA: Bi-EDTA: Bi-EDTA: Bi-EDTA: 2.33 mg/l 3.3 mg/l 1.61 mg/l 3.24 mg/l Other Fe-citrate: Cu-EDTA: Cu-EDTA: Cu-EDTA: 8.86 mg/l 5 mg/l 5 mg/l 7.5 mg/l Fe-citrate Fe-citrate: Fe-citrate: 8.86 mg/l 2.215 mg/l 4.43 mg/l Bi: metal Bi/Fe: Bi/Cu/Fe: Bi/Cu/Fe: Bi/Cu/Fe: ratio 0.26 1/0.66/0.37 1/0.322/0.72 1/0.432/0.731 Deposition Time 6.9 h 5 h 5 h 5 h parameters Mean current 1.5 A/dm² 1.5 A/dm² 1.5 A/dm² 1.5 A/dm² density Form of Direct current Direct current Direct current Direct current current Temp. 65° C. 65° C. 65° C. 65° C. Substrate Type/quantity Built-up post Plaster Plaster Inner made from stumps; stumps; telescope made gold-titanium conductive conductive from a dental alloy; silver silver gold casting conductive alloy filled silver with Pattern Resin (from GC); conductive silver Deposition Thickness 300 μm 200 μm 200 μm 200 μm result Gold content >99.9% >99.9% >99.9% >99.9% Bi content Bi < 40 ppm Bi < 40 ppm Bi < 40 ppm Bi < 40 ppm Alloy content Fe < 10 ppm Fe < 10 ppm Fe < 10 ppm Fe < 10 ppm Efficiency of 86% 86% 86% 86% the bath Appearance gold colored, gold colored, gold colored, gold colored, silk finish; shiny; smooth shiny; smooth shiny; smooth smooth Functionality defect-free; defect-free; defect-free; defect-free; stable during stable during stable during stable during firing of the the subsequent the subsequent the ceramic ceramic or ceramic or subsequent veneer and plastic plastic processing suitable for veneering veneering and fully cementing to functional as the implant a secondary build-up post part 

1. Bath, preferably aqueous bath for the electrodeposition of gold and gold alloys, in which the gold is in the form of a gold sulfite complex, characterized in that the bath contains at least one bismuth compound, preferably at least one water-soluble bismuth compound, and if appropriate at least one compound of at least one further metal and standard additives for gold sulfite baths of this type.
 2. Bath according to claim 1, characterized in that the gold sulfite complex is an ammonium-gold sulfite complex.
 3. Bath according to claim 1 or claim 2, characterized in that it has a pH of >7, preferably from 7 to
 9. 4. Bath according to one of the preceding claims, characterized in that it contains copper as a further metal.
 5. Bath according to one of the preceding claims, characterized in that it contains iron as a further metal.
 6. Bath according to one of the preceding claims, characterized in that it contains at least one precious metal, preferably at least one precious metal from the platinum group, as a further metal.
 7. Bath according to one of claims 4 to 6, characterized in that it contains at least one water-soluble bismuth compound and at least one water-soluble copper compound.
 8. Bath according to claim 5 or claim 6, characterized in that it contains at least one water-soluble bismuth compound and at least one water-soluble iron compound.
 9. Bath according to one of claims 4 to 8, characterized in that it contains at least one water-soluble bismuth compound, at least one water-soluble copper compound and at least one water-soluble iron compound.
 10. Bath according to one of the preceding claims, characterized in that the bismuth compounds and preferably also the compounds of the further metals are complex compounds, preferably chelate compounds.
 11. Bath according to claim 10, characterized in that the complex compounds contain organic complex-forming agents, preferably organic chelate-forming agents.
 12. Bath according to claim 11, characterized in that the complex-forming agents or chelate-forming agents are NTA, HEDTA, TEPA, DTPA, EDNTA or in particular EDTA.
 13. Bath according to one of the preceding claims, characterized in that the bismuth compounds are present in the bath in a concentration of between 0.05 mg/l and their saturation concentration.
 14. Bath according to claim 13, characterized in that the bismuth compounds are present in the bath in a concentration of between 0.05 mg/l and 1 g/l in particular between 0.1 mg/l and 10 mg/l.
 15. Bath according to one of the preceding claims, in particular according to one of claims 1 to 14, characterized in that the compounds of the further metals are present in the bath in a concentration of between 0.1 mg/l and 200 g/l, preferably between 0.1 mg/l and 500 mg/l.
 16. Bath according to claim 15, characterized in that the compounds of the further metals are present in the bath in a concentration of between 1 mg/l and 20 mg/l, preferably between 2 mg/l and 10 mg/l.
 17. Bath according to one of the preceding claims, characterized in that it is substantially free of physiologically harmful additives, preferably is free of arsenic, antimony and thallium compounds.
 18. Bath according to one of the preceding claims, characterized in that the gold is present in the bath in a concentration of between 5 and 150 g/l.
 19. Bath according to claim 18, characterized in that the gold is present in the bath in a concentration of between 10 and 100 g/l, preferably between 10 and 50 g/l, in particular between 30 and 48 g/l.
 20. Use of a bath according to one of the preceding claims for the production of prosthetic moldings for the dental sector by means of electrodeposition, in particular for the production of dental frames, such as crowns, bridges, superstructures and the like.
 21. Use of at least one bismuth compound, preferably of at least one water-soluble bismuth compound, for the production of prosthetic moldings for the dental sector by means of electrodeposition, in particular as a constituent of a bath according to one of claims 1 to
 19. 22. Use according to claim 21, characterized in that the bismuth compound is a complex compound, in particular chelate compound, which preferably contains an organic complex-forming agent or chelate-forming agent.
 23. Use according to claim 22, characterized in that the complex-forming agent or chelate-forming agent is NTA, HEDTA, TEPA, DTPA, EDNTA or in particular EDTA.
 24. Use according to one of claims 21 to 23, characterized in that the bismuth compound is added directly during preparation of the bath.
 25. Use according to one of claims 21 to 23, characterized in that the bismuth compound is added to the bath immediately before or during the electrodeposition.
 26. Use according to one of claims 21 to 25, characterized in that the bismuth compound is added to the bath after an electrodeposition step for top-up purposes.
 27. Use according to one of claims 20 to 26, characterized in that the prosthetic molding is deposited in a layer thickness of more than 10 μm, preferably in a layer thickness of between 100 and 300 μm, in particular in a layer thickness of approx. 200 μm.
 28. Process for producing prosthetic moldings for the dental sector from gold and gold alloys by electrodeposition, in particular for the production of dental frames, such as crowns, bridges, superstructures and the like, characterized in that a gold or gold alloy layer is deposited from a bath according to one of claims 1 to 19 on a suitable substrate, e.g. on a cast which has been molded from a tooth stump, and is then separated from the substrate.
 29. Process according to claim 28, characterized in that the substrate is composed of an electrically nonconductive material, in particular plaster or plastic, the surface of which has been made conductive, in particular with the aid of conductive silver.
 30. Process according to claim 28, characterized in that the substrate is composed of at least one metal.
 31. Use or process according to one of claims 20 to 30, characterized in that the deposition takes place at high current densities, preferably at current densities of up to 10 A/dm².
 32. Use or process according to one of claims 20 to 31, characterized in that the deposition takes place using what is known as the pulse-plating process.
 33. Use or process according to one of claims 20 to 32, characterized in that the prosthetic molding is veneered with ceramic and/or plastic.
 34. Use or process according to claim 33, characterized in that a molding veneered with ceramic is fired.
 35. Use or process according to claim 33, characterized in that a molding veneered with plastic is cured using light, in particular using visible light. 